This invention relates, in general, to the manufacture of semiconductor integrated circuits, and more particularly, to the manufacture of a semiconductor device having a pattern delineation on its surface.
In the manufacture of integrated circuits, particularly bipolar integrated circuits, it is common to form a localized buried layer prior to the growing of an epitaxial layer. The buried layer is typically used as a collector in a bipolar integrated circuit. The buried layer is conventionally formed by a diffusion or by an ion implantation process. Ion implantation tends to damage the surface of the substrate thereby requiring annealing to repair such damage.
In the manufacture of these devices the buried layer is formed as an enhanced doped region in the surface of a semiconductor substrate. After this formation, an epitaxial layer is grown over the substrate which also covers the buried layer. During subsequent processing of the integrated circuit it is important to know the exact location of the buried layer so that other required elements of the integrated circuit can be formed in proper relationship. A common method practiced to delineate the location of the buried layer is to indent the region containing the buried layer. This is typically done by etching the region containing the buried layer prior to the growth of the epitaxial layer. In order to do this the surface of the semiconductor substrate must be protected in order to prevent simultaneously etching the surface of the substrate. One method which is disclosed in U.S. Pat. No. 4,389,255 which issued to Chen et al. on June 21, 1983, is to provide an oxide layer over the semiconductor substrate with an opening defining the buried layer region. Polysilicon is then grown over the oxide and buried layer region. Dopant is then diffused through the polysilicon layer to form the buried layer. Once the buried layer is formed the polysilicon is oxidized which at the same time causes some oxidation of the buried layer region. By oxidizing the polysilicon layer it is converted to oxide which is then removed with the first layer of oxide leaving a semiconductor surface having a recessed buried layer region.
Another method practiced in the past was to protect the semiconductor substrate by using a layer of silicon nitride while the buried layer region was being etched. This method required a considerable number of processing steps. First oxide is grown over the substrate, then the oxide is covered with nitride which has to be scrubbed before photoresist can be used. The resist is spun on, exposed, developed, baked, etc. The nitride is then etched through openings provided in a photoresist layer which define the buried layer region. Then the oxide in the buried layer region also has to be etched. When the etching is completed then the photoresist is stripped off. During subsequent processing to form the buried layer, the silicon nitride occasionally would chip or flake off and contaminate the buried layer region in the surface of the semiconductor substrate. This contamination reduced the yield of the devices.
By now it should be appreciated that it would be desirable to provide a process for forming buried layers which simplifies processing of the semiconductor substrate and at the same time does not induce contaminates.
Accordingly, it is an object of the present invention to provide an improved method for obtaining pattern delineation of a buried layer.
Another object of the present invention is to provide a process for obtaining buried layer pattern delineation by simplifying the processing of the semiconductor substrate.
A further object of the present invention is to provide a method for obtaining buried layer pattern delineation in a reduced time cycle while obtaining higher yields.
Yet another further advantage of the present invention is to provide a method for obtaining a recessed enhanced doped area on the surface of a semiconductor substrate.